Am I wrong thinking that most of a tyres resistance comes from the carcass movement, not from the actual friction of the contact patch with the ground. And surely a rough surface will test the carcass in a completely different way than a smooth roller? Meaning that the tire conforms to the roads variable shape, and that shape is not the same as a the perfectly even one of a smooth roller.

Ofcourse, if the end result is the same, as was claimed here and I don't doubt or dispute that fact, and that difference doesn't matter, then there is not point in testing things that way. But that was sort of my way of reasoning here...

I avoided posting anywhere else, because it was already taking too much time to maintain the slowtwitch thread... but what the hell.

Testing for Crr on a smooth roller can only give you the energy loss due to tire casing hysteresis and deflection. On the road, surface roughness and hardness also play a role. I'm not measuring that... only the tire deflection component. A 1.5x factor is applied to the measurements to bring them more in line with field test results for a smooth road. On a rough road the losses would be much higher.

Even though the contact patch on an 80mm roller is very different (and the resistance much higher) than it is on the road, the results can be scaled to smooth road conditions. I'm frankly surprised that it works this well, but the people who have done meticulous and difficult field testing to isolate Crr have seen the same relative Crr difference as on roller tests. And roller tests are much easier to perform accurately.

I agree the data will provide a ranking that will be the same in the real world. Tests like this have to be done under controlled conditions otherwise the data is worthless. WNW what are the errors in the data or do you not know.

I did 4 repeats of Conti SS 20mm dispersed over 2 days and the max scatter was less than 2%. I'm happy with that. I'll know more about it after I've retested more tires. If you are wondering how much of an error there is in translating the numbers to on-road Crr, it appears to be low enough that the roller results are valid for making comparisons.

There are other factors I need to get refined like the temperature effect on Crr. I'm using .6%/F currently, which is what I read in Bicycling Science. I normalize to a fixed ambient temperature because I figured the temperature difference would be nil on the road. Tom Anhalt thinks the effect is larger based on his testing... and also believes no correction should be applied at all since the tire would heat up on the road also. I still doubt that there will be much of a difference between the tire temperatures on the road, but that is something I can test.

It's no more than a wild guess but I suppose Conti historically opted for a lower TPI count in order to prevent the sidewalls from being cut too easily.

Even now I still own some tubular tyres which do not have any anti-puncture belt whatsoever. They ride amazingly well and provided you avoid urban trash areas they do not puncture any more or less than a more "modern" tyre. They're not even anything special as they come with a butyl tube and are dirt cheap too. Incredibly comfortable, even more so than a Veloflex Carbon at the same pressure. All that with a butyl inner tube.As you would expect, that particular model has been phased out just recently only to be replaced by one that does come with a PRB which, would you believe, adds 50g per tyre. I want a gun. A big one.....

All this makes you wonder what could be made if someone really put some effort in it and build a real racing tyre. Tubular and clincher, no frills just speed.

Sure, it would be great if the impact of a PRB, TPI count and the nature of a compound could be tested thouroughly and individually but how?AFAIK all PRB have a negative impact on weight, Crr and comfort. Most aren't even that effective to start with.Casing's TPI, higher is better and how many times in a lifetime do we slash a sidewall anyway?Compound? Other than Black Chili (excellent in wet conditions) I'd say keep it KISS. Veloflex's natural rubber is a fine example.And what's the impact of vulcanizing over glueing, thread profiles versus slick?

Sure, it would be great if the impact of a PRB, TPI count and the nature of a compound could be tested thouroughly and individually but how?

Continental's top tires all have the same casing material. The GP4000 has thicker tread and a Vectran belt... the Attack, Force and the TT tire all have thinner tread and a Vectran belt... although I'm not certain if the tread compound or Vectran belts are slightly different (probably not)... and the Supersonics have thin tread and no Vectran belt.

When Continental came out with the Black Chili compound, their rolling resistance went from bad to good. I think the tread compound was the only change. Plus the BC tread has good traction and great longevity. The only negative is that it seems to not ride as smoothly.

The test is fundamentally flawed. There is no correlation between a tire on a smooth surface versus a rough surface. Roads are never a smooth surface so the results are meaningless.

As a thought experiment, take a hard solid rubber tire. It will have incredibly low resistance on a smooth surface and incredibly high energy loss on a rough surface. With this test, the solid tire would still be predicted to be the most efficient on a rough surface. Sorry but completely flawed.

i really commend WMW and others who are putting their time and hearts into these comparisons and making the data available. i said the same over in the slowtwitch thread, but i'm hopeful that i can carve out some time to post data from a number of tires i own and use frequently -- including some vittoria clinchers as well as a number of tubulars (continental, vittoria, fmb, dugast). could be interesting.

i think there is quite a bit to be learned from this testing.

that said, while i want to believe that the order and magnitude of difference as exhibited on a roller scale linearly to rougher roads, i'm just not sure i'm there. i see references to "careful tests" that prove this, but i've never seen any of these tests (and i've been looking for a while, though perhaps in the wrong places). i'm open to the possibility that i am wrong.

i tend to agree with sedluk's point of view. if you take an extreme example (a tire that will not deform at all; hypothetical) it might rank #1 there but would fair poorly on the world's worst road. i notice that reference to "the real world" generally suggest that the roller results scale to smooth roads. hm.

while this example is extreme, this leads me to believe that there is somewhere along the spectrum between "smooth road" and "world's worst road" where the correlation to the rollers breaks down. would it be on chip seal? that's real world where i ride and race. also, there are different grades of chip seal.

i think the further trouble i have is that tires have different properties, some of which allow the tire to be more flexible at higher pressures -- or some allow the rider to run lower pressures without risking pinch flats. i know there must be an attempt to standardize, but comparing all tires at the same pressure may mean that some (all?) tires are running at sub-optimal pressures. this example becomes clear if you compare Crr on the rollers for a 19mm tire vs a 25. on the road one would never choose the same pressure for both, given a constant rider weight.

doing this kind of testing would be even more tedious. an example: do many runs with tires at 5psi increments to find the lowest Crr for each. then, compare those "optimal" conditions to one another.

still doesn't solve the chip-seal road issue -- but that could be done by creating/modifying a roller.

Did you read the thread Sedluk? Separate data have suggested that as you increase pressure rolling resistance decreases, up to a break point where it increases sharply because compliance is important on rough roads. A solid tyre may well be a completely difficult case. However, previous data has also suggested that the rank order of rolling resistance determined by this method is preserved when the tyres are tested outside on real roads. Commercial testing labs use this method.

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